Derived　from　double-walled　carbon　nanotubes,　graphene　quantum　dots　(GQDs)　with　a　uniform　size　distribution　were　prepared　through　solution　chemistry.　The　GQDs　in　chlorobenzene　exhibited　bright　blue　emission　upon　UV　excitation.　The　introduction　of　the　GQDs　into　a　bulk　heterojunction　polymer　solar　cell　based　on　poly(3-hexylthiophene):(6,6)-phenyl-C61　butyric　acid　methyl　ester　(P3HT:PCBM)　resulted　in　a　significant　enhancement　of　the　power　conversion　efficiency　(PCE).　The　efficiency　was　further　improved　by　adjusting　the　PCBM　content　in　the　active　layer,　reaching　a　maximum　PCE　of　5.24%.　This　ternary　system　based　on　blended　P3HT:PCBM:GQDs　represents　a　new　method　to　enhance　the　efficiency　of　polymer　solar　cells.　©　2013　Nature　Publishing　Group.